The invention relates to a laser waveguide medium which can be used as a laser waveguide, in particular a laser channel waveguide, to provide light amplification of laser oscillation. The invention further relates to a waveguide laser containing a laser waveguide medium, a method of manufacturing a laser waveguide medium, as well as a method of generating light amplification or laser oscillation using a laser waveguide medium.
Integrated optical circuitry is a rapidly growing field of technology having benefits in such areas as signal processing, computers, sensors, spectroscopy and communications. Integrated optical circuits, as the name implies, provide for the integration of multiple optical components on a single substrate. For example, an integrated optical circuit (IOC) can comprise a laser, switches, polarizers, detectors, etc. IOC's are used, for example, in optical data processing and optical sensing, as well as optical communications. See Integrated Optical Circuits and Components: Design and Applications, edited by L. D. Hutchenson (1987).
The use of miniature solid-state lasers such as diode pump solid-state lasers and fiber lasers in integrated optics is known. The miniature diode pumped solid-state lasers are small, compact and lightweight lasers in which a monolithic block of solid active laser material, usually crystalline, is pumped using a diode as the pump light source. A typical material for such a compact solid state laser is neodymium-doped YAG (yttrium aluminum garnet). This laser system emits at 1064 nm. Fiber laser systems, on the other hand, typically contain erbium-doped silica-based fibers which are produced by CVD processes. These fiber laser systems generally operate at a wavelength of about 1.54 .mu.m. Neodymium-doped fibers that lase at 1060 nm have also been demonstrated. Due to spectroscopic limitations, light amplification at 1.3 .mu.m is not possible in silica optical fiber laser systems. Light amplification at 1310 nm has been achieved in praseodymium-doped heavy metal fluoride optical fibers. This glass is known as ZBLAN. Light amplification around 1410 nm has been achieved in neodymium-doped phosphate fibers. Also, light amplification and lasing has been achieved in neodymiumdoped LiYF.sub.4 (Nd:YLF) at 1315 nm.
Light amplification in the region of 1.3 .mu.m is particularly desirable for miniature solid-state laser oscillators and amplifiers for telecommunication applications. The vast majority of optical fiber communication systems operate near this wavelength.
There are two primary wavelengths that are used for optical fiber telecommunications, 1.3 .mu.m and 1.55 .mu.m. The 1.55 .mu.m band is used for undersea optical fiber links because silica optical fibers have their lowest attenuation at that wavelength. The 1.3 .mu.m band is used because silica optical fibers have their lowest dispersion at that wavelength. That means that very high bandwidth signals can be transmitted at this wavelength without the pulse broadening caused by dispersion. Detectors that operate at these wavelengths are made from Group III-V materials such as InGaAs. These detectors, as well as the laser sources, are costly to manufacture. Silicon detectors are much less expensive to produce than Group III-V detectors, but their response only extends to 1.1 .mu.m in the infrared.
If the length of this optical fiber network is relatively short, and if moderate bandwidths are required, it is possible and perhaps desirable to operate the network at other wavelengths, where the sources and detectors are less costly. Efficient waveguide lasers that operate at 1.06 .mu.m can be useful for networks such as these. Such networks can find application in aircraft, ships, automobiles, or cable television distribution.
Integrated optic laser oscillators and amplifiers have also been produced using laser glass substrates, i.e., neodymium-doped laser glass. Such devices employing silicate glasses operate at wavelengths near 1057 nm and, in phosphate glasses, operate at wavelengths near 1057 nm and 1355 nm. See, e.g., Sanford et al., Opt. Lett., 15:366 (1990); Sanford et al., Opt. Lett. , 16 (14) :1095; Sanford et al., Opt. Lett., 18 (4) :281 (1993); Aoki et al., IEEE Photon. Tech. Lett., 2:459 (1990); and Aoki et al., Elec. Lett., 26:1910 (1990). However, efficient lasing with high output power and high efficiency has not been achieved at these wavelengths.
U.S. Pat. No. 5,080,503 discloses an optical waveguide device in which a waveguide, embedded in a substrate, contains a rare earth element and can be used as a laser, i.e., at the emission wavelength of the rare earth element. The waveguide region is embedded into the substrate by first depositing a film onto the substrate surface by an evaporation process. Through the use of a mask, openings are provided in the film, thereby exposing portions of the substrate surface. The substrate in then immersed in a molten salt and the waveguide region is formed by ion exchange. For example, the substrate can be immersed into a molten salt bath. The exchange of ions from the salt bath into the substrate will form the waveguide region.
U.S. Pat. No. 4,993,034 discloses a laser waveguide medium exhibiting a peak wavelength at 1.054 nm. See FIGS. 9 and 10. The optical waveguide region is formed in a laser glass substrate by an ion exchange procedure. In the ion exchange, alkaline ions are exchanged for other ions. In particular, Ag.sup.+ ions are exchanged for Na.sup.+ ions in the substrate. Alternatively, Cs.sup.+ ions can be exchanged for K.sup.+ ions in the substrate. The laser glass substrate contains 0.01-8 mole % Na.sub.2 O or 0.01-18 mole % K.sub.2 O. Amounts of Na.sub.2 O greater than 8.0 mole % lead to deterioration of chemical durability. Thus, when the Na.sub.2 O content of the substrate exceeds 8 mole %, a crack or distortion can occur in the substrate during the ion exchange procedure. Also, excess Ag.sup.+ ion exchange is said to occur resulting in silver colloid formation.